1. Field of the Invention
The present invention relates, generally, to a contamination control system. More particularly, the present invention relates to a contamination control system for simultaneously and efficiently controlling various contaminants and an air-conditioning system of a substrate processing apparatus using the contamination control system.
2. Description of the Related Art
Generally, a process line for manufacturing a part, for example a semiconductor device or an electronic article, may be contaminated by various contaminants. Even a very small amount of contaminants, such as a unit of parts per billion (ppb), reduces the yield and productivity of semiconductor fabricating equipment. Thus, it is required to provide a gaseous environment having a high degree of purity to the semiconductor fabricating equipment. In particular, as semiconductor devices have become more highly integrated, it is increasing more important to prevent an airborne molecular contamination (AMC), as well as a typical particle contaminates, from contaminating the semiconductor devices during manufacturing. For example, the contaminants including the AMC and the particle may cause the following phenomena: a native oxide layer may be formed on a substrate due to the presence of an ozone contaminate, a photoresist pattern of light amplification type may have a profile having a T-top shape due to the presence of an ammonia contaminate, a critical dimension currently issued in the semiconductor fabricating process may vary, and a tolerance of a gate oxide layer may be deteriorated due to the presence of an organic material.
Accordingly, the semiconductor fabricating process ought to be carried out under a clean atmosphere. The semiconductor fabricating equipment is disposed in a clean room. The semiconductor fabricating equipment is also surrounded by a casing. A clean air supplying apparatus such as a fan filter unit (FFU) is connected to the clean room. The FFU includes a fan and a filter, which are integrated. Processing units of the semiconductor fabricating equipment are disposed under the clean air supplying apparatus so that clean air produced from the clean air supplying apparatus is provided to the processing units. A chemical filter is connected to the clean air supplying apparatus. The chemical filter removes O3, NH3, SOx, NOx and an organic substance contained in a flow of air that is introduced into the semiconductor fabricating equipment. Conventionally, contamination control has focused on a metal contaminant and a particle contaminant. A conventional air filter may remove a particle having a size of below about 0.1 μm.
However, the chemical filter is very expensive and short-lived. Thus, since the chemical filter is periodically exchanged for a new chemical filter, the running cost of the clean air supplying apparatus increases, thereby increasing the cost of the semiconductor device. Further, since various chemical filters are provided in accordance with various contaminants, maintenance of the chemical filters may be difficult. This causes continuous use of a disabled chemical filter so that trouble may occur in the semiconductor fabricating process. When a new AMC appears, a new chemical filter for removing the new AMC is required, and the cost associated with developing the new chemical filter increases the cost of the new filter needed to remove the new AMC.
Further, the AMC in the clean room, which is referred to as an ambient contamination, may be chemically non-visual. Thus, the AMC may not be studied from the viewpoint of the contamination control technology. Accordingly, a control system for removing the AMC may not be developed.
Meanwhile, methods for removing contaminants in a flow of air using a wet air-conditioning type have been proposed using a water showering system instead of the chemical filter and are disclosed in Korean Patent No. 0340334 and Japanese Patent Laid Open Publication No. 1998-340851.
FIG. 1 is a schematic view illustrating a conventional contamination control system. Referring to FIG. 1, a conventional contamination control system using a water showering system includes a spray unit 10 having a plurality of nozzles that spray water, preferably deionized water, in the form of water droplets, an eliminator 20 for dropping the water droplets by colliding the water droplets against the eliminator 20, and a tank 25 for collecting the dropped water droplets and for containing the collected water droplets until the collected water droplets are provided to the spray unit 10. Air (Ai) introduced into the spray unit 10 is changed into clean air (Ao) through the eliminator 20. In FIG. 1, dotted arrows represent the direction of the flow of the air and solid arrows represent the directions of the flow of the water in the contamination control apparatus.
The water is introduced into the tank 25 by a pump (not shown). The water is provided to the spray unit 10 through a filter 30. The water rapidly passes through the nozzles and exits the nozzles in the form of a water droplet. The water droplet passes through the eliminator 20 having a porous plate (not shown) to capture contaminants in the air (Ai). The water droplet collides with the porous plate and then drops into the tank 25. The water droplet is collected in the tank 25 and remains in the tank 25 until water from the tank 25 is provided to the spray unit 10.
According to the conventional water showering system, the contaminants are removed by adsorbing suspended dust in the water droplet. The more contaminants are captured by the water, the more the water in the tank 25 is contaminated. As a result, when the water continues to circulate, the quality of the water deteriorates. That is, the water becomes as contaminated as the air so that efficiency for capturing the contaminants from the air is reduced. For example, the circulating water may have efficiency for removing below about 60% of NOx, about 50% of an organic substance and about 20% of ozone in the air. Thus, there is a limit to the amount of contaminants that can be removed using the circulating water. In addition, the pH of the circulating water is lowered by the contaminants such that the circulating water having a low pH may not remove the contaminants from the air.
FIGS. 2 and 3 are graphs showing a relation between the pH of the circulating water and the removal efficiency of the water. In the FIGS. 2 and 3, curved lines A1 and B1 represented the pH of the circulating water and curved lines A2 and B2 represented the removal efficiency with respect to SO42−. It should be noted that the removal efficiency is closely related to the pH of the circulating water.
FIG. 4 is a graph showing variations of the pH of the circulating water with respect to time. It should be noted that the pH of the circulating water was gradually augmented proportional to a lapse of time.
The removal efficiency of the conventional water showering system is shown in following Table 1.
TABLE 1RemovalWind velocityefficiency (%)(m/sec)pHContaminantsNH381.001.286.17NOx64.00SOx88.00Organic50.00Ozone16.80
To prevent the reduction of the removal efficiency of the circulating water, the contaminants are diluted and the pH of the circulating water is maintained. These may be accomplished by continuously providing above about 90% of new water to the tank 25 through a supply line 22 and by also draining the same amount of contaminated water through a drain line 24. However, when an amount of the new water is too much, a load cost and a running cost of the pump 30 increase so that the water showering system has an inferior efficiency. Therefore, the conventional water showering system may not be employed in an air-conditioning system of a piece of equipment used in semiconductor fabrication.